The present invention relates to a solid electrolytic capacitor element in which the edge part of a valve-acting metal substrate having on the surface thereof a dielectric film acts as the anode, and an insulating layer having a predetermined width is circumferentially provided on the substrate to come into contact with the anode part. On the entire surface of the substrate on the side opposite the anode with respect to the insulating layer, a solid electrolyte layer comprising an organic material such as electrically conducting polymer or an inorganic material such as metal oxide and further thereon an electrically conducting layer are sequentially formed to work out to the cathode. The present invention also relates to a method for producing the capacitor element; and a solid electrolytic capacitor using the element.
With the progress of digitization and high frequency processing of electronic instruments for reducing the size, saving electric power and the like, there is an increasing demand for a solid electrolytic capacitor having low impedance at a high frequency, high reliability and high capacitance.
As a capacitor satisfying these capabilities, a capacitor using a tantalum sintered body or an aluminum foil for the anode and a solid electrolyte formed of an electrically conducting polymer having high electrical conductivity or an inorganic oxide for the cathode is commercially available. Particularly, a chip-type capacitor that is surface-mounted on an electronic circuit board is designed to employ a highly heat-resistant material capable of enduing the heat of reflow soldering or to have a structure capable of relieving thermal stress. However, the above-described solid electrolyte is poor in the capability of repairing the dielectric film, although the resistance is low, and in some cases, the dielectric film is macroscopically broken due to thermal stress to increase the leakage current.
An object of the present invention is to construct a solid electrolytic capacitor element having a capability of relieving the thermal stress generated in the reflow soldering or the like to prevent an increase of leakage current and to provide a solid electrolytic capacitor favored with low impedance and high reliability.
The outline of the solid electrolytic capacitor element of the present invention is described below by referring to FIG. 1 showing a cross section.
In FIG. 1, (1) is a valve-acting metal substrate (anode substrate) having on the surface thereof a dielectric film (2), (3) is an insulating layer having a predetermined width and circumferentially provided on the valve-acting metal substrate, (4) is a solid electrolyte layer, (5) is a carbon paste layer, and (6) is a metal powder-containing electrically conducting layer.
The solid electrolytic capacitor of the present invention, by which the described-above objects can be attained, has a structure such that the metal powder-containing electrically conducting layer (6) constituting the cathode part does not contact with the insulating layer (3) which works out to the boundary with the anode part, while preventing increase in the resistance of the metal powder-containing electrically conducting layer (6). More specifically, a spacing (t1) is provided between the cathode side edge part (3a) of the insulating layer and the insulating layer side edge part (6a) of the metal powder-containing electrically conducting layer to prevent the metal powder-containing electrically conducting layer (6) to run beyond the region of the carbon paste layer (5), so that electrical conduction can be reduced in the vicinity thereof and an increase in leakage current can be prevented.
Furthermore, a structure for preventing the increase in ESR (equivalent series resistance) is also employed, where the relative ratio of the spacing (t1) between the cathode side edge part (3a) of the insulating layer and the insulating layer side edge part (6a) of the metal powder-containing electrically conducting layer to the length (t0) of the cathode part (7) is specified.
In the embodiment constructed as such, a substance having high electrically conductivity (the metal powder-containing electrically conducting layer) is not present in the vicinity of the insulating layer and the metal powder-containing electrically conducting layer is kept apart from the insulating layer. Therefore, even when the insulating layer is partially broken under mechanical or thermal stress, the electrical conduction hardly occurs in the vicinity thereof and the leakage current does not increase.
The term xe2x80x9ccircumferentially providedxe2x80x9d as used in the present specification means to encompass a certain site. The term xe2x80x9cplaced onxe2x80x9d is not limited only to the vertical relationship but includes the state where two substances are disposed to contact each other. The term xe2x80x9cjoinxe2x80x9d means to connect and bond two members.
That is, the present invention provides a solid electrolytic capacitor element, a method for producing the capacitor element, and a solid electrolytic capacitor, which are described below.
(1) A solid electrolytic capacitor element comprising (1) a valve-acting metal substrate having on a surface thereof a dielectric film with an edge part acting as an anode, (2) an insulating layer circumferentially provided on said valve-acting metal substrate, (3) a solid electrolyte layer and (4) an electrically conducting layer comprising a carbon paste layer and a metal powder-containing electrically conducting layer, said solid electrolyte layer and said electrically conducting layer being formed in this order on an entire surface of the substrate on a side opposite said anode with respect to the insulating layer and acting as a cathode part, wherein said metal powder-containing electrically conducting layer is provided within a region of the carbon paste layer, such that said metal powder-containing electrically conducting layer does not contact the insulating layer.
(2) A solid electrolytic capacitor element comprising (1) a valve-acting metal substrate having on a surface thereof a dielectric film with an edge part acting as an anode, (2) an insulating layer circumferentially provided on said valve-acting metal substrate, (3) a solid electrolyte layer and (4) an electrically conducting layer comprising a carbon paste layer and a metal powder-containing electrically conducting layer, said solid electrolyte layer and said electrically conducting layer being formed in this order on an entire surface of the substrate on a side opposite said anode with respect to the insulating layer and acting as a cathode part, wherein said metal powder-containing electrically conducting layer is provided with a spacing from a cathode side edge part of said insulating layer.
(3) The solid electrolytic capacitor element as described in 2 above, wherein the spacing between said metal powder-containing electrically conducting layer and the cathode side edge part of said insulating layer is about {fraction (1/10)} or more but less than xc2xd of the entire length of said cathode part.
(4) The solid electrolytic capacitor element as described in 2 or 3 above, wherein the spacing between said metal powder-containing electrically conducting layer and the cathode side edge part of said insulating layer is from about 0.1 to about 1.5 mm.
(5) The solid electrolytic capacitor element as described in 1 above, wherein said metal powder-containing electrically conducting layer comprises an electrically conducting filler comprising metal powder, and a fluororubber as a main component of a binder.
(6) The solid electrolytic capacitor element as described in 5 above, wherein about 80% by mass or more of the binder is fluororubber.
(7) The solid electrolytic capacitor element as described in 5 above, wherein about 80% by mass or more of the electrically conducting filler is silver powder.
(8) The solid electrolytic capacitor element as described in 5 above, wherein said metal powder-containing electrically conducting layer comprises from about 50 to about 95% by mass of the electrically conducting filler and from about 5 to about 50% by mass of the binder.
(9) The solid electrolytic capacitor element as described in 1 above, wherein the carbon paste layer comprises an electrically conducting carbon material, a binder and a solvent as main components, about 80% by mass or more of said electrically conducting carbon material is an artificial graphite, and said binder comprises a material having rubber elasticity.
(10) The solid electrolytic capacitor element as described in 1 above, wherein the valve-acting metal has a plate or foil shape.
(11) The solid electrolytic capacitor element as described in 1 above, wherein the valve-acting metal is an elemental metal selected from the group consisting of aluminum, tantalum, niobium and titanium, or the valve-acting metal is an alloy of said elemental metal.
(12) The solid electrolytic capacitor element as described in 1 above, wherein the solid electrolyte layer comprises an electrically conducting polymer layer.
(13) The solid electrolytic capacitor element as described in 12 above, wherein the electrically conducting polymer layer comprises a polymer of a 5-member heterocyclic ring-containing compound.
(14) The solid electrolytic capacitor element as described in 13 above, wherein the 5-member heterocyclic ring-containing compound comprises a structure of bivalent thiophene skeleton.
(15) The solid electrolytic capacitor element as described in 12 above, wherein the electrically conducting polymer layer comprises poly(3,4-ethylenedioxythiophene).
(16) A solid electrolytic capacitor obtainable by placing at least one capacitor element as described in any one of 1 to 15 on a lead frame and joining these.
(17) A method for producing a solid electrolytic capacitor element, comprising a valve-acting metal substrate having on a surface a dielectric film; circumferentially providing an insulating layer on a position defining an edge part acting as an anode of the valve-acting metal substrate; and sequentially forming a solid electrolyte layer and an electrically conducting layer comprising a carbon paste layer and a metal powder-containing electrically conducting layer on an entire surface of the substrate on a side opposite said anode with respect to said insulating layer, wherein said metal powder-containing electrically conducting layer is provided within a region of the carbon paste layer, such that said metal powder-containing electrically conducting layer does not contact the insulating layer.
(18) A method for producing a solid electrolytic capacitor element, comprising a valve-acting metal substrate having on a surface a dielectric film; circumferentially providing an insulating layer on a position defining an edge part acting as an anode of the valve-acting metal substrate; and sequentially forming a solid electrolyte layer and an electrically conducting layer comprising a carbon paste layer and a metal powder-containing electrically conducting layer on an entire surface of the substrate on a side opposite said anode with respect to said insulating layer, wherein said metal powder-containing electrically conducting layer is provided with a spacing from a cathode side edge part of said insulating layer.